1. Field of the Invention
This invention relates to differential gears having a differential motion limiting function.
2. Description of the Related Art
Among automobile differential gears, those (called limited slip differentials) having a differential motion limiting function, and fashioned so that, when the wheel on one side only tries to freewheel, adequate turning force is still transmitted to the wheel on the other side through clutch means, are widely employed in order to prevent the loss of adequate turning force to the wheel on one side when the wheel on the other side freewheels because it is on ice, snow, or mud or the like, and to prevent the auto-body fishtailing phenomenon when executing a turn or quick getaway or the like.
The differential gears 100 diagrammed in FIG. 14, for example, are described in Japanese Patent Publication No. S55-27980/1980 (published) and in Japanese Patent Application Laid-Open No. S58-221046/1983 (published). These differential gears 100 comprise a pair of pressure rings 103 deployed inside a differential case 101 so as to freely move in the direction of wheel axles 102 but be incapable of relative turning, a pinion shaft 104 deployed perpendicularly to the wheel axles 102 in a condition wherein the shaft end is held between the pressure rings 103, a pinion gear 105 deployed so as to freely turn on the pinion shaft 104, a pair of side gears 106 deployed to the left and right wheel axles 102, respectively, so as to be incapable of relative turning, which side gears 106 sandwich the pinion gear 105 and mesh with the pinion gear 105 on either side thereof, actuation means 108 that, in response to increases in relative turning torque between the pinion shaft 104 and the differential case 101 during differential motion, activate the pressure rings 103 in a direction such that the clearance 107 between the pressure rings 103 becomes greater, and clutch means 109 deployed on both sides of the pair of pressure rings 103 in the wheel axle direction, which clutch means 109 limit the differential motion of the left and right wheel axles 102 as the clearance 107 actuated by the pressure rings 103 becomes larger.
For the actuation means 108, various shapes are proposed. In one example thereof which is adopted, a cam unit 110 having a square shape one diagonal whereof is set in the wheel axle direction is formed on one shaft end of the pinion shaft 104, and a substantially V-shaped cam channel 111 into which the cam unit 110 engages is formed in the pressure rings 103.
In the differential gears 100, moreover, when relative turning torque occurs between the pinion shaft 104 and the differential case 101, the clearance 107 between the pressure rings 103 will widen due to the actuation means 108, and, thereby, the clutch means 109 will be activated and the differential motion of the left and right wheels will be limited, but the configuration is made so that, in order that the clearance 107 between the two pressure rings 103 will return to a set interval at normal times, elastic members 112 such as plate springs are positioned outside of the two sets of clutch means 109 in the wheel axle direction, so that the pressure rings 103 are urged in a direction such that they approach each other through a plurality of clutch plates 113 of the clutch means 109.
Now, in differential gears 100 such as this, it is necessary to secure sufficient area in the friction pressing portion of the clutch plates 113 in order that the differential motion of the left and right wheels will be definitely limited by the clutch means 109 in a differential motion limiting condition. However, the size of the differential case 101 is restricted by the positional relationship between the differential gears 100 and various equipment on the automobile side, making it very difficult to establish that size larger than what it is currently. For that reason, it has been virtually impossible to obtain a more adequate differential motion limiting action than what is obtained currently by increasing the number of clutch plates 113 or making their size larger.
In a horizontal engine vehicle, in particular, as compared to an inline engine vehicle, more severe restrictions are imposed by the layout of the engine and the parts peripheral thereto, and the shape and capacity of the differential case are sharply restricted. As in the differential gears 120 diagrammed in FIG. 15, for example, it is necessary to diminish the diameter of the left portion of the differential case 121, making it very difficult to establish satisfactorily large area in the friction pressing portion of the clutch means 122. In addition, when the urging force of the elastic members 123 is increased in order to increase the friction pressing force, it becomes impossible to obtain a differential motion condition while effecting a slow turn, as described earlier, wherefore it has been impossible to obtain adequate differential motion limiting action.
The applicant, as a result of assiduous investigations into how to adequately secure friction pressure force in clutch plates, discovered that, whereas configuring the clutch means deployed on either side of the two pressure rings in the wheel axle direction in left-right symmetry was established as one design condition in conventional differential gears, the same kind of differential motion limiting action could be obtained even with one member of the clutch means omitted. Thereupon, the applicant proposed differential gears such as the differential gears 120A diagrammed in FIG. 16, wherein clutch means 122A are only deployed between the left portion of a differential case 121A having room to spare and the wheel axle 102 on the left side.
However, even in these differential gears 120A, a problem developed in that, depending on the shape of the differential case 121A, with a differential case 121B wherein the right portion is given a large diameter, as indicated by the imaginary lines in FIG. 16, for example, a comparatively large portion of wasted material is formed in the right portion of the differential case 121B. Besides that, moreover, in the differential gears 100, 120, and 120A described in the foregoing, a side wall 103a is formed which extends to the vicinity of the sleeves of the side gears 106 in the pressure rings 103 in order to catch substantially the entire side surface of the clutch plates 113, but the applicant discovered that the number of clutch plates 113 becomes fewer precisely by the measure of the thickness t of the side wall 103a, and that there still exists ample leeway for enhancing the friction pressure force of the clutch plates 113.
In differential gears such as described above, moreover, it is desirable that, fundamentally, a differential motion condition ensue wherewith maneuvering in tight places can be done when making low-speed turns such as when garaging a vehicle or parallel parking, and that, when one wheel is freewheeling, or a quick getaway is being made, or when turning at high speed or under heavy loading, a differential motion limiting condition ensue wherewith stable initial performance is obtained.
With conventional differential gears, however, as seen in the differential gears 100, for example, given the relationship whereby the left and right pressure rings 103 are urged by elastic members 112 in a direction such that they will approach each other, via the clutch plates 113, when the urging force is set to be weak, manipulating the clutch means 109 by the actuation means 108 becomes easy, whereupon there are cases where a differential motion limiting condition will ensue even when making a low-speed turn, and the differential motion condition will not stabilize, whereas, when the urging force is made strong, the actuation means 108 reach a condition where differential motion is possible, but, due to the urging force of the elastic members 112, the clutch plates 113 are normally friction pressed, and attain a substantially differential motion limiting condition, as a consequence whereof a differential motion condition cannot after all be stably secured during low-speed turning. In other words, problems arise in that either the ability to maneuver in tight places during low-speed turning suffers, or the so-called chattering phenomenon occurs wherewith the differential motion limiting condition and differential motion condition switch back and forth, controllability deteriorates, and the differential gears 100 and equipment peripheral thereto are adversely affected by shocks during chattering.
For this reason, setting the urging force is very difficult. In a competition vehicle wherewith sport driving is presupposed, for example, what is currently done is that controllability during low-speed turns is to some extent sacrificed, and the urging force of the elastic members 112 is set on the high side in a configuration wherewith an adequate differential motion limiting condition can be realized at high speed or under heavy loading.
An object of the present invention is to provide differential gears wherewith adequate differential motion limiting action can be obtained even under heavy loading and wherewith also a differential motion condition and differential motion limiting condition can be suitably switched between.
The applicant, as a result of assiduous investigations into how to increase the area of the friction pressing portion in clutch means, arrived at the idea of it being possible to omit the side wall 103a of the pressure rings 103 in the differential gears 100 and 120 diagrammed in FIGS. 15 and 16, and deploy clutch plates within the thickness t of the side wall 103a, and thereby were able to perfect first and second differential gears relating to the present invention.
A first embodiment of differential gears relating to the present invention comprise: a differential case that is turned by the drive force from the engine about the left and right wheel axles; a pair of left and right side gears deployed, respectively, at the ends of the left and right wheel axles, so as to be incapable of relative turning; a pair of left and right pressure rings deployed inside the differential case so as to freely move in the direction of the wheel axles, but be incapable of relative turning, and so as to cover the outer circumferential sides of the left and right side gears, respectively, the inner diameter of at least one of the pressure rings being set larger than that of the side gears; a pinion shaft deployed perpendicularly to the wheel axles with the ends thereof held between the left and right pressure rings; at least one pair of pinion gears that are deployed so as to turn freely on the pinion shaft, and mesh with the left and right side gears; a set of clutch means that are deployed on both sides of the two pressure rings in the direction of the wheel axles, and comprises first clutch plates fitted into the differential case so as to move freely in the direction of the wheel axles but be incapable of relative turning, and second clutch plates fitted over the sleeves in the side gears so as to move freely in the direction of the wheel axles but be incapable of relative turning, the first and second clutch plates being deployed alternately so that the clutch means are capable of limiting the differential motion of the left and right wheel axles by limiting the relative turning of the differential case and the side gears by friction between the first and second clutch plates; urging means for urging the two pressure rings in a direction such that the clearance between the two pressure rings narrows; and actuation means for actuating the pressure rings against the urging force of the urging means, in a direction such that the clearance between the two pressure rings increases, in accordance with increases in the relative turning torque between the pinion shaft and the differential case during differential motion, and activating the clutch means.
In this first embodiment of differential gears, when the turning resistance on the left and right wheels is the same, the pinion gears, side gears, pinion shaft, and pressure rings turn integrally with the differential case, and the left and right wheels turn at the same speed. When the turning resistance on the two wheels differs, however, the pinion gears revolve while meshing with the side gears due to a portion of the turning force acting on the differential case, and a differential motion condition is switched to wherewith the turning speed of the wheel on the side of lower turning resistance becomes faster than the turning speed of the wheel on the side of higher turning resistance is switched to, or a differential motion limiting condition is switched to wherewith the relative turning of the side gears and differential case is limited by the clutch means, and a portion of the turning torque acting on the differential case is distributed toward the wheel affected by larger turning resistance.
More specifically, when the turning resistance on the left and right wheels differs, in response to the relative turning torque between the pinion shaft and the differential case due to the actuation means, the actuation force in the direction wherewith the clearance between the two pressure rings increases acts on both pressure rings. However, when the actuation force produced by these actuation means is smaller than the urging force produced by the urging means, the clearance does not change, and a normal differential motion condition is obtained, whereas, when that force becomes larger than the urging force, the clearance between the two pressure rings becomes larger in response thereto, and the clutch plates of the clutch means are friction pressed against each other, whereupon the differential motion of the left and right wheels will be limited.
Now, in the first embodiment of differential gears, because the inner diameter of at least one of the pressure rings is set larger than the diameter of the side gears, it is possible to configure the pressure rings so that the material thickness thereof is thin in the axial direction, making it possible to increase the number of clutch plates that can be accommodated by that measure. Furthermore, while it is permissible to set the inner diameter of only one pressure ring larger than the diameter of the side gears, in order to increase the number of clutch plates accommodated as much as possible, it is preferable that the inner diameters of the left and right pressure rings be set larger than the diameters of the side gears.
A second embodiment of differential gears relating to the present invention comprise: a differential case that is turned by the drive force from the engine about the left and right wheel axles; a pressure ring deployed inside the differential case so as to freely move in the direction of the wheel axles but be incapable of relative turning, and so as to cover the outer circumferential side of one of the side gears noted above, the inner diameter of the pressure ring being set larger than that of the side gear; a pinion shaft deployed perpendicularly to the wheel axles with the ends thereof held between the pressure ring and the surface of the differential case facing the pressure ring; at least one pair of pinion gears, deployed so as to turn freely on the pinion shaft, that mesh with the left and right side gears; clutch means that are deployed on the side of the pressure ring opposite to the surface facing the pressure ring, and comprises first clutch plates fitted into the differential case so as to move freely in the direction of the wheel axles but be incapable of relative turning, and second clutch plates fitted over the sleeves in the side gears so as to move freely in the direction of the wheel axles but be incapable of relative turning, the first and second clutch plates being deployed alternately so that the clutch means are capable of limiting the differential motion of the left and right wheel axles by limiting the relative turning of the differential case and the side gears by friction between the first and second clutch plates; urging means for urging the pressure ring in a direction such that the clearance between the pressure ring and the surface facing the pressure ring narrows; and actuation means for actuating the pressure ring against the urging force of the urging means, in a direction such that the clearance between the pressure ring and the surface facing the pressure ring increases, in accordance with increases in the relative turning torque between the pinion shaft and the differential case during differential motion, and activating the clutch means.
In the second embodiment of differential gears, in basically the same way as in the differential gears described in claim 1, switching is effected between a non-differential motion condition wherein the left and right wheels turn at the same speed, a differential motion condition wherein the turning speed of the wheel on the side of lower turning resistance becomes faster than the turning speed of the wheel on the side of higher turning resistance, and a differential motion limiting condition wherein a portion of the turning torque acting on the differential case is distributed toward the wheel affected by the higher turning resistance.
More specifically, when the turning resistance on the left and right wheels differs, in response to the relative turning torque between the pinion shaft and the differential case due to the actuation means, the actuation force in the direction wherewith the clearance between the pressure ring and the ring opposing surf ace increases acts on the pressure ring. However, when the actuation force produced by these actuation means is smaller than the urging force produced by the urging means, the clearance does not change, and a normal differential motion condition is obtained, whereas, when that force becomes larger than the urging force, the clearance between the pressure ring and the ring opposing surface becomes larger in response thereto, and the clutch plates of the clutch means are friction pressed against each other, whereupon the differential motion of the left and right wheels will be limited.
Also, because the inner diameter of the pressure ring is set larger than the diameter of the side gear, it is possible to configure the pressure ring so that the material thickness thereof is thin in the axial direction, making it possible to increase the number of clutch plates that can be accommodated by that measure.
In the second embodiment of differential gears, furthermore, because only one set of clutch means need be incorporated, in addition to being able to make the differential gears easier to assemble, it is now possible to incorporate clutch means on the side thereof which has room to spare, making it possible to set the size of the clutch plates as large as possible and enhance the friction pressure force while configuring the differential gears in a small size. For that reason, the differential gears can be used suitably with engines designed for horizontal mounting wherein the restrictions on differential case shape and size are severe. Furthermore, when only one set of clutch means is provided in this manner, the relative turning between the one side gear and the differential case will be directly limited by the clutch means, while the relative turning between the other side gear and the differential case will be limited by the clutch means via the pinion and one side gear.
The applicant also arrived at the idea of it being possible to make clutch means deployed to both sides of the two pressure rings in the direction of the wheel axles in a left-right asymmetrical configuration wherein differences are imparted in the number of sets of clutch plates and/or in the outer diameters thereof, and thereby was able to perfect a third embodiment of differential gears relating to the present invention.
The third embodiment of differential gears relating to the present invention comprise: a differential case that is turned by the drive force from the engine about the left and right wheel axles; a pair of left and right pressure rings deployed inside the differential case so as to freely move in the direction of the wheel axles but be incapable of relative turning; a pinion shaft deployed perpendicularly to the wheel axles with ends thereof held between the two pressure rings; at least one pair of pinion gears deployed so as to turn freely on the pinion shaft; a pair of left and right side gears, deployed at the axle ends of the left and right wheel axles, respectively, so as to be incapable of relative turning, and so as to sandwich the pinion gears and mesh with the pinion gears on both sides thereof; a set of left and right clutch means that are deployed on both sides of the two pressure rings in the direction of the wheel axles, and are capable of limiting the differential motion of the left and right wheel axles by limiting the relative turning between the differential case and the side gears, the outer diameters and/or the number of clutch plates per set being different between the left and right clutch means; urging means for urging the two pressure rings in a direction such that the clearance between the two pressure rings narrows; and actuation means for actuating the pressure rings against the urging force of the urging means, in a direction such that the clearance between the two pressure rings increases, in accordance with increases in the relative turning torque between the pinion shaft and the differential case during differential motion, and activating the clutch means.
In this third embodiment differential gears, in the same way as in the first embodiment, switching is effected between a non-differential motion condition wherein the left and right wheels turn at the same speed, a differential motion condition wherein the turning speed of the wheel on the side of lower turning resistance becomes faster than the turning speed of the wheel on the side of higher turning resistance, and a differential motion limiting condition wherein a portion of the turning torque acting on the differential case is distributed toward the wheel affected by the higher turning resistance.
Also, because a difference is imparted in the outer diameters and/or the number of sets of clutch plates in the two sets of clutch means, it is possible to adjust the outer diameters or number of sets of clutch plates according to the shape of the differential case, and, while avoiding a portion of wasteful material thickness from being formed in the differential case, to incorporate clutch plates in the differential case without gaps, whereupon the area of the friction pressure portion of the clutch plates is increased as much as possible, and adequate differential motion limiting action is obtained even under heavy loading.
Here, in addition to differentiating the diameters of the clutch plates between the left and right clutch means in the third embodiment of differential gears, splines are provided for fitting clutch plates inside the differential case so as to move freely in the axial direction but be incapable of relative turning, and the pitch of the splines for the clutch plates of smaller diameter may be set larger than the pitch of the splines for the clutch plates of larger diameter. That is, the portion of the differential case wherein the clutch plates of small diameter are fit is small in diameter and on the back side of the differential case, and spline machining workability for that portion is not very good. It is therefore preferable that the pitch of the small-diameter clutch plates be set larger than the pitch of the large-diameter clutch plates, in a configuration that reduces the work involved in machining the splines for the differential case.
It is also permissible to set the inner diameter of at least one of the pressure rings larger than the diameter of the side gears. When that is the case, because the inner diameter of that at least one pressure ring is set larger than the diameter of the side gears, it is possible to configure the pressure ring with a thin material thickness in the axial direction, making it possible to increase the number of clutch plates that can be accommodated by that measure. Furthermore, while it is permissible to set the inner diameter of only one pressure ring larger than the diameter of the side gears, in order to increase the number of clutch plates accommodated as much as possible, it is preferable that the inner diameters of the left and right pressure rings be set larger than the diameters of the side gears.
In the first, second, and third embodiments of differential gears, it is preferable that collars be provided which are fitted over the sleeves of the side gears such that those collars are incapable of relative turning, and that, for the clutch means, use be made of means having first clutch plates fit into the differential case so that they move freely in the direction of the wheel axles but are incapable of relative turning, and second clutch plates fit over the side gear collars so that they move freely in the direction of the wheel axles but are incapable of relative turning. In other words, it is also possible to form splines or the like in the side gear sleeves and assemble the second clutch plates therewith so as to move freely in the axial direction but be incapable of mutual turning, but, because of the machining difficulties involved in forming splines all the way to the gears of the side gears, it is preferable to assemble collars comprising separate members with the sleeves of the side gears, and then mount the second clutch plates so that they fit thereover.
When that is done, it is also preferable that the collars be configured so as to have substantially the same diameter as the side gears but be smaller in diameter than the inner diameter of the pressure rings, and that the ends of the collars be inserted inside the pressure rings. When the configuration is made in that way, the second clutch plates are definitely prevented from coming off of the collars on the side toward the gears of the side gears.
In the first, second, and third embodiments of differential gears, furthermore, for the urging means, it is preferable that urging means be provided which urge the pressure rings in a direction such that the clearance narrows, without the intervention of the clutch means. When that is the case, the clutch plates of the clutch means will not be friction pressed even when the urging force of the urging means is set high, and the timing of the switching from the differential motion condition to the differential motion limiting condition will be made dependent only on the actuation force of the actuation means and the urging force of the urging means. Thus it becomes possible to make the configuration such that, by setting the urging force of the urging means properly, the differential motion condition is definitely obtained during low-speed turning, and the differential motion limiting condition is definitely obtained when turning at high speed or under heavy loading.